Method for recovering a substantially olefin-free hydrocarbon fraction



Feb. 4, 1947.

J. T. HohEczY 2,415,171 METHOD FOR RECOVERING A SUBSTANTIALLY OLEFIN-FREE HYDROCARBON FRKCTION Filed Dec. 1, 1943.

mm a Fud g Boron Trlfluorldc a A c llll v i Acetic Acid Frucflomno' I xi A XI Oloflnjgo Fioctlon Patented Feb. 4, 1947 METHOD FOR RECOVER-INS: A SUBSTAN- TIALLY OLEFIN-FREE HYDROCARBON FRACTION Joseph T. Horeczy, Baytown, Tex., assignor to Standard Oil Development Company, a corporation of Delaware Application December 1, 1943, Serial No. 512,494

The present invention is concerned with a method for treating olefinic hydrocarbon frac-' tions. More particularly, itrelates to a method for removing olefins from'olefin-containing hydrocarbons by treatment of such fractions with organic acids in the presence of boron halide catalystswhereby the olefinic hydrocarbons are converted to the corresponding esters and the non-olefinic hydrocarbons are recoverable in purified form.

In many refinery operations the removal of olefins from hydrocarbon fractions is accomplished by treating the olefin-containing fraction with strong sulfuric acid. This method is commonly referred to' as acid treating, and while it is effective in reducing the olefin content of the hydrocarbon fraction in question and has received wide adoption by the industry, this method of treating results in consumption of large quantities of sulfuric acid and, the formation of trou-' blesome amounts of acid sludge. The olefins are substantially lost in the acid sludge and the acid sludge itself presents a handling problem to the petroleum refiner. j I

In the present invention the olefinic hydrocar bons normally lost when acid treating was employedin their removal from other hydrocarbons, are madeavailable and recovered as organic esters of the acid used and the hydrocarbon involved. These esters have valuable properties as solvents and find wideusage in the arts. Furthermore, the unreacted hydrocarbons are then recoverable substantially free of olefins by simple distillation methods.

Briefly the present invention involves the reaction of oleflnic hydrocarbons, dissolved in a suitable solvent, with organic acids in the presence of a boron halide. Acids which have been found suitable for carrying out the present invention are acetic acid and acids of the same homologous series, such as formic, propionic and butyric. In addition other organic acids, such as benzoic, salicylic andtoluic may also be used. As a specific example, acetic acid maybe used as the organic acid and boron trifiuoride as the boron halide. 1

Prior investigators of the reaction between olefins and organic acids in the presence of boron trifiuoride were unsuccessful in obtaining substantial yields of esterified products unless excep- .6 Claims. (Cl. 196-39) 2 other than the esters increased directly with the amount of catalyst employed. Furthermore, it was found that a considerable amount of the boron trifiuoride was disssolved in the ester as it was formed, and the boron trifluoridewas thereby made inactive by absorption in the ester which resulted in the yield of ester remaining constant for the particular percentage of boron trifluorlde employed.

The early workers employing the reaction between olefins and organic acids in the presence of boron trifluoride investigated the use of the organic acid dissolved in a solvent. It was their finding that selection of an appropriate solvent required much study. Most of the common oxygenated solvents were impractical to use in the reaction since stable compounds often resulted. Chlorinated hydrocarbons were effective to some extent but the results obtained indicated that polymerization of the olefins was promoted rather than esterification of the organic acid. To the present inventors knowledge, a suitable solvent for the reaction was not disclosed in the prior art teachings.

In the present invention the disadvantages inherent in the prior teachings have been largely overcome. This beneficial result is attained by conductingthe reaction in the presence of a hydrccarbon diluent, which for convenience may be the olefin-containing fraction itself since the olefins are obtained normally in association with other hydrocarbons such as the parafllns naphthenes and aromatics. Thus a hydrocarbon fraction containing the olefins having six carbon atoms in the molecule would also contain the corresponding paraflfins, naphthenes and aromat ics which compounds serve as'admirable diluents for the reaction.

It has been found that high yields of esters may 7 ence to the attached drawing in which the single figure is a flow diagram of one method of conductiniz the invention.

gators found that when boron tr'lfiuoride in encess of about 10% was used to catalyze the reaction, the quantity of residual heavy v material Reierringnow to the drawinmnumeral I l designates a storage tank tor a hydrocarbon. fraction containing olefins such'as a hexane-hexylene fraction. Storagetank l l is connected by way of line I2 and pump 13 with reactor l4. Reactor It is provided with a stirring device l5 which is actuated by prime mover I 6. The olefin-containing hydrocarbon is introduced into a reactor Hi from storage tank II in the manner described and is admixed therein with a complex of boron trifluoride and acetic acid; The boron trifiuoride is conducted to the reactor from the storage tank ll via line I9, pump 20, and line 2|. Acetic acid is withdrawn from tank #8 through line 22 by pump 23 and injected into line 2| and thence to 'may be employed. Under these conditions one phase results which is removed from the reactor M by line 24 for further treatment, as will be described hereinafter. The ratio of boron fluoride to acetic acid will vary Widely depending on the olefin content of the hydrocarbon fraction and the number of carbon atoms in the olefin, but generally a mole ratio from about 1:2 to 1:10 may be employed. A ratio of boron trifiu'oride to acetic acid of'122 has been found to give good results. V

It is desirable that the olefin-containing hydrocarbon should be added to the reactor it throughout the period of contact to insure formation of the esters rather than polymerization of the olefins. An excess of the organic acid over the hydrocarbon is'required for best results. It

. is preferred to maintain a ratio of organic acid hydrocarbon of the order of about 3:1 to about 5.1.

The reactant mixture is discharged from reactor M by line 25 and is introduced thereby'into fractionator 25. While in this particular instance fractionator 25 has been shown as a single distillation tower, it is to be understood that it may comprise several distillation towers as desired.

amounts oi these heavy hydrocarbons is substantially suppressed.

While the stream removed from fractionator 25 by line 30 maybe recycled to reactor I4 through line 2|, it may be more desirable to withdraw this stream from the system by opening valve 32 and subject it to distillation conditions for recovery of the esters and then to recycle the ester-free heavy material to reactor l4 to suppress formation of additional amounts of heavy hydrocarbons. This extra distillation step on the esterified fraction is not shown in the drawing, but the invention is not necessarily limited to the particular distillation.

embodiment described therein.

The present invention may be practiced with a variety of olefimcontaining feed stocks. For example, it may be employed with a feed stock containing the butylenes, pentylenes, 'hexylenes and the like. while-it may be used to remove olefins from toluene concentrates. The present invention has particular utility in reducing the olefin content of catalytically cracked naphthas whereby the isoparafiins contained therein are easily recoverable by distillation.

The amount of olefins contained a particular fraction to be treated in accordance with the present invention should not exceed about 75%. -In cases where fractions are employed which contain more than this amount of olefins it is within the spirit and scope of the present invention to dilute the olefinic content of the hydrocarbon fraction by addition of a nonolefin hydrocarbon such as a paraflin, an aromatic or anaphthene. Of course, when the olefin content of the hydrocarbon fraction is diluted by addition of an extraneous hydrocarbon, it is desirable to employ a hydrocarbon having a boilingpoint dissimilar to the hydrocarbon to be treated 'to make the extraneous hydrocarbon diluent easily recoverable from the reactants by The present invention will be further described by reference to the following examples.

In the present instance fractionator25 is equipped with line 26 for removal of gaseous boron trifiuoride, line 27 for removal of unreacted acetic acid and line 28 for recovery of olefin-free hydroc arbon. Fractionator 25 is also provided with heating means 29 for adjustment of temperature and pressure conditions therein and with line 30 for discharge of residual boron trifluoride-acetic acid complex, esters, and polymers or any. alkylated materials which may form.

The boron trifluoride removed from fractionator 25 by line 25 returns to storage tank 1? for reuse while the unreacted acetic acid returns by way of line 27 tostorage tank it.

Connected to line 30 is line 25 provided with pump 31 for recycle of heavy material and boron trifiuoride-acetic acid complex to reactor M. Line 30 is provided with valve 32 byway of which build-up of heavy material in the system is avoided by periodically discharging a portion of the heavy hydrocarbons formed during the reaction. This fraction contains the esters which may be recovered therefrom by further treatment such as by distillation.

It may be mentioned at this point that recycling of the heavy material formed in the reaction to the reactor It is beneficial since it has been found that by continually recycling 9. portion of the heavy hydrocarbons, formation of additional Example 1.-A hydrocarbon fraction boiling between and 168 F. in the amount of 125 volumes was contacted with a complex of boron fluoride and acetic acid, one mole of the hydrocarbonfraction' being contacted with 1 /2 moles of boron fluoride in 3 moles of acetic acid. The fraction having the-above boiling point characteristics contained 60 weightper centof olefins and 40 weight per cent of paraffins and naphthenes. This fraction 'Was added over a period of two hours to the well-stirred complex with the reaction mixture being maintained at a temperature between and F. throughout the reaction. After the two-hour reaction period the reacting mixture comprised a homogeneous phase. The reactants were cooled to room temperature, and the mixture waswashed with dilute sodium carbonate solution; the resulting hydrocarbon layer wasthen separated from the carbonate'solution and distilled. The hydrocarbon layer before distillation amounted to 100 volumes of oily product. On distillation of the hydrocarbon layer there wererecovered 30 volumes of unreacted hydrocarbons, 50 volumes of esters,

and 20 volumes of polymers. The theoretical yield of esters was 120 volume per cent, while 70' per cent of the theoretical was-- obtained in this run. -7 5 per cent of the saturated hydrocarbon content were recovered, indicating that a portion of the saturates reacted with a portion of the olefinic content of the charge to form greatly in excess of that obtainable when opera ating in accordance with the prior art.

Example 2.--In another operation a hydrocarbon fraction boiling between 200 and 250 F.

which contained per cent olefins, per cent toluene and 35 per cent of parafiins and naph- I thenes,. was treated with boron fluoride-acetic acid complex as described in Example 1. After the reaction time of two hours had been completed the homogeneous product was washed with sodium carbonate and the oily hydrocarbon layer separated and recovered. The yield of the hy-. drocarbon layer amounted-"to 100 volumes. Analysis of the recovered hydrocarbon layer by precise fractional distillation showed that 63 per cent by volume of the hydrocarbons, 18 per cent .by volume of esters, and 19 per cent by volume of polymers were obtained. I'heyield of hydrocarbons based on the original non-olefin hydrocarbon content of the fraction charged showed that per cent of thetheoretical amount of material were recovered and that /2 per cent of the toluene contained in the original fraction were recovered substantially free of olefins. The theoretical yield of estersobtainable if the reaction had proceeded without formation of polymerized or condensed products'was volume per cent. The yield of esters actually obtained was 50 per cent of the theoretical.

The'above operations indicate that fractions substantially free of olefins may be obtained by proceeding in accordance with the present invention while recovering larger yields of esters than by Letters Patentis:

1. A method for recovering a, substantially olefin-free hydrocarbon fraction comprising the geneous phase, withdrawing the homogeneous phase and subjecting it to distillation conditions to recover a hydrocarbon fraction substantially free from oleflns.

2. A process in accordance with'claim 1 in which the feed stock boils within the range of to'168-F. and contains 60% oleflns and 40% paraflins and naphthenes.

3. Aprocess in accordance with claim 1 in which the feed stock boil-s inthe range of 200 to 250 F. and contains 30% olefins, 35% toluene and 30% paraflins and naphthenes.

4. A method for recovering a substantially 'olefin-free hydrocarbon fraction comprising the steps of contacting a hydrocarbon feed stock comprising olefin in an amount not in excess of 75% with a. complex of acetic acid and boron trifiuoride at a temperature in the range of to F., while maintaining a ratio of from 3 to 5 moles of acetic acid per mole of hydrocarbon feed stock-to form a homogeneous phase, withdrawing the homogeneous phase from'the contacting step and subjectingit to distillation conditions to recover a hydrocarbon fraction substantially free from olefins.

. 5. A method in accordance with claim 4 in which the complex consists of one mole of boron trifluoride per two moles of acetic acid and the hydrocarbon feedstock boils in the range of 140 to 168 F. and contains approximately 60% oleflns and 40% parafiins and naphthenes.

6. A method in accordance with claim 4 in which the complex is composed of one mole of boron'trifluoride per two moles of acetic acid and the feed stock boils within the range of 200 to 250 Pr and contains approximately 30% oleflns,

35% toluene and 35% parafilns and naphthenes.

JOSEPH T. HORECZY.

REFERENCES cI'rEp The following references are of record in the file "of this patent:

steps of contacting. a hydrocarbon feed stock inof acid per mole of feed stock to form a homo- UNITED STA'I'ES PATENTS Date Number Name 2,065,540 Schneider Dec. 29, 1936 2,006,734 Edlund et al. July 2, 1935 1,365,052 Ellis et al Jan. 11, 1921 1,790,521 Davis et a1. 1; Jan. 2'7, 1931 2,356,357 Schlesman et al. Aug. 22. 44 2,133,452 

